Add "Deactivate/Activate budget" functionality

[chadoh]

• [ ] When deactivate is selected, a confirmation modal will be displayed. If the user clicks the “Deactivate” button in the confirmation modal, a transaction signing panel will be opened (maybe skip this; see discussion in Google Doc; if we can skip this, then remove the currently-commented-out code)
• [ ] Functionally, deactivate means setting the budget to 0. We should enhance the radspec to conditionally display a different message when the _amount is zero. E.g. Deactivate "Marketing" budget

[javieralaves]

Looks good, but as of right now the 'New allocation' option is still there when it shouldn't, and the icon is not the correct one. I presume this is currently being addressed by @chadoh's latest update.

[javieralaves]

Tested this on the continuous deploy from December 17th, 2019.

✅ Looks great!